If you’ve don nothing to customize this, shame on you :-). If the user has no previous version of Silverlight installed at all, they’ll be presented with whatever your default “not installed” experience is. Here’s a few scenarios for you – keeping in mind the information below is related to the application being build in Silverlight 3: No Silverlight installed, Silverlight 3 installed, Silverlight 1/2 installed and a note about the plugin MIME type. So what does this mean to you when you put a sample out for people to see in your organization or perhaps if you have a preview of a product or something and users visit this application. We’ve not integrated the end-user upgrade/install into the template for now. The only way people can view Silverlight 3 content during this Beta phase is by having one of the versions of the developer runtime for either Windows or Mac installed. What this means is that we don’t recommend putting things in production as we’ve not exposed or wired up the end-user runtime for Silverlight 3.
In the release of Silverlight 3 Beta, we noted that this is a developer release and that no “Go Live” licensing was going to be available for this release.
If you are like any other developer, including me, you probably disregard most warnings and are usually the same type that keeps clicking next when installing things without paying attention to detail.